Method of making a bullet-resistant transparent panel

ABSTRACT

A method of making a transparent panel is provided. The transparent panel effectively blocks the penetration of a bullet when fired from one side of the panel, but not when fired from the other side of the panel. The method comprises forming a sheet of acrylic resin and a sheet of polycarbonate resin, both of equal size and configuration. A sealing strip is applied completely around the peripheral edge of one of the sheets and the two sheets are then brought together, being spaced apart by the sealing strip. Two holes are then drilled into one of the two sheets at locations spaced at diagonally opposite corner edges of the sheet. Under pressure applied to the opposite faces of the two sheets, a liquid resin is injected into the space between the two sheets through one of the two holes until the entire volume between the two sheets is filled. Then the resin is permitted to harden. In an alternative method, the pressure is applied to the opposite faces of the two sheets using a fixed and a movable frame assembly. Each of the frame assemblies comprise a plurality of parallel pressure bars extending transversely across the respective frame.

This is a divisional of application Ser. No. 07/843,337, filed on Feb.28, 1992 now U.S. Pat. No. 5,229,204.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a bullet-resistant transparent panel,and also to a method and presses for making such a panel.

Many types of bullet-resistant transparent panels are known. One type,as described for example in U.S. Pat. No. 4,594,290, includestransparent sheets of acrylic and polycarbonate resins bonded togetherby a transparent polyurethane adhesive. The invention of the presentapplication is directed particularly to the latter type ofbullet-resistant transparent panel.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a transparent panel,particularly of the type described in U.S. Pat. No. 4,594,290,exhibiting unidirectional bullet-resisting characteristics; that is, thepanel blocks the penetration of a bullet when fired from the outer sideof the panel, but not when fired from the inner side of the panel.

Another object of the invention is to provide a method of makingtransparent panels, and a further object is to provide a pressparticularly useful for making such transparent panels.

According to the present invention, there is provided a transparentpanel effective to block the penetration of a bullet when fired from theouter side of the panel but not when fired from the inner side of thepanel, the transparent panel comprising: an outer transparent sheet ofan acrylic resin having a thickness of 7.5-9 mm, and an innertransparent sheet of a polycarbonate resin having a thickness of 9.5-11mm, the sheets being bonded together by a polyurethane transparentadhesive.

It has been surprisingly found, as will be shown more particularlybelow, that when the acrylic and polycarbonate sheets are of the abovethicknesses, the laminated panel exhibits unidirectionalbullet-resisting characteristics. Such a panel construction thusprovides protection against outsiders attacking persons inside anenclosure, such as a vehicle, a protective teller's cage, or the like;but at the same time the panel permits insiders to fire against theattacking outsiders.

Best results were obtained when the outer acrylic resin sheet has athickness of about 8 mm, the inner polycarbonate resin sheet has athickness of about 10 mm, and the transparent polyurethane adhesive hasa thickness of about 2 mm.

According to another aspect of the present invention, there is provideda method of making a transparent panel, comprising forming a sheet of anacrylic resin and a sheet of a polycarbonate resin of the same size andconfiguration; applying a sealing strip around the peripheral edge ofone of the sheets; applying the other sheet over the one sheet with thetwo sheets spaced from each other by the sealing strip; drilling twoholes through one of the sheets adjacent its diagonally opposite edges;applying pressure to the opposite faces of the two sheets to press themagainst the sealing strip; injecting under pressure an adhesive liquidthrough one hole of the one sheet until it exits from the other holethereof; and permitting the adhesive to harden to bond the two sheetstogether.

According to a still further aspect of the present invention, there isprovided a press for laminating a plurality of sheets, comprising: afixed frame assembly, and a movable frame assembly movable with respectto the fixed frame assembly; each of the frame assemblies including aplurality of parallel pressure bars extending transversely across therespective frame; the press further including a plurality of adjustabledevices for precisely positioning the pressure bars against the oppositesurfaces of the panel.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 illustrates a flat transparent panel constructed in accordancewith the present invention;

FIG. 2 illustrates a curved transparent panel constructed in accordancewith the present invention;

FIG. 3 illustrates the manner of precurving each of the resin sheets inmaking the curved panel of FIG. 2;

FIG. 4 illustrates the method of laminating the two resin sheetstogether in order to produce the curved panel of FIG. 2;

FIG. 5 illustrates a press useful in making the flat panel of FIG. 1 orthe curved panel of FIG. 2;

FIG. 6 is an enlarged fragmentary view of the press of FIG. 5; and

FIG. 7 is a fragmentary view illustrating another press useful in makinglaminated panels in accordance with the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The bullet-resistant panel illustrated in FIG. 1 is constituted of anouter transparent sheet 2 of an acrylic resin, an inner transparentsheet 3 of a polycarbonate resin, and a transparent polyurethaneadhesive 4 between the two sheets bonding them together to form anintegral panel.

The acrylic resin sheet 2 has a high degree of hardness, but is somewhatbrittle. On the other hand, the polycarbonate resin sheet 3 is less hardthan the acrylic resin sheet, but is also less brittle. By using thecombination of the two sheets to form the panel, the outer acrylic resinsheet 2 imparts a high degree of hardness to the outer face of the panelreceiving an impact, such as a bullet, rock or the like, and attenuatesthe force of this impact; whereas the polycarbonate resin sheet 3 on theinner face of the panel absorbs the attenuated force and supports theacrylic resin sheet 2 against breaking or shattering. The combination ofthe two sheets thus provides a high degree of resistance againstpenetration or shattering by bullets, stones, rocks or the like.

It has been surprisingly found that the panel illustrated in FIG. 1 canbe provided with unidirectional bullet-resisting characteristics if thetwo resin sheets 2 and 3 are made of predetermined thicknesses. Thus, bymaking the outer acrylic resin sheet 2 of a thickness of 7.5-9 mm, andthe inner polycarbonate resin sheet 3 of a thickness of 9.5-11 mm, thepanel has been found to block the penetration of a 9 mm bullet whenfired from the side of the outer acrylic resin sheet, but not when firedfrom the side of the inner polycarbonate resin sheet.

Table 1 below summarizes the results of a number of tests that wereconducted on laminations of polycarbonate and acrylic sheets ofdifferent thicknesses when impacted by a bullet shot from an Uzi 9 mmfull metal jacket (FMG); velocity 359.6 m/sec; distance of 3 meters;temperature of 17°-25° C. at time of test:

                  TABLE 1                                                         ______________________________________                                                       RESULTS                                                                                         Shot from                                              POLYCAR-   Shot from   Polycarbonate                                ACRYLIC   BONATE     Acrylic Side                                                                              Side                                         ______________________________________                                        1.  8 mm       6 mm      Passed through                                                                          Passed through                             2.  8 mm       8 mm      Blocked but                                                                             Passed through                                                      produced a                                                                    "mushroom"                                                                    deformation                                                                   in the poly-                                                                  carbonate side                                       3.  8 mm      10 mm      Blocked   Passed through                             4.  8 mm      12 mm      Blocked   Blocked                                    5.  6 mm      10 mm      Passed through                                                                          Passed through                             6.  10 mm     10 mm      Blocked   Blocked                                    ______________________________________                                    

The polycarbonate sheet was that supplied by Tsutsunaka of Japan underthe trademark Sunloid PC; and the acrylic sheet was a cast acrylic sheetsupplied by Mitsubishi of Japan, the polycarbonate and acrylic sheetshaving the properties as set forth in the following Table 2:

                  TABLE 2                                                         ______________________________________                                        Properties    Polycarbonate                                                                              Acrylic                                            ______________________________________                                        Specific gravity                                                                            1.2          1.20                                               Rockwell hardness                                                                           R119         R124                                               Tensile strength                                                                            650 kgf/cm.sup.2                                                                           720-770 kgf/cm.sup.2                               Elongation    85%          4-7%                                               Compressive strength                                                                        830 kgf/cm.sup.2                                                                           160-250 kgf/cm.sup.2                               Flexural strength                                                                           950 kgf/cm.sup.2                                                                           1100-1200 kgf/cm.sup.2                             Flexural modulus                                                                            24000 kgf/cm.sup.2                                                                         30000-31000 kgf/cm.sup.2                           Izod impact strength                                                                        80 kgf · cm/cm                                                                    2-3 kgf · cm/cm                           Heat deflection                                                                             135° C.                                                                             87-100° C.                                  temperature                                                                   Coefficient of linear                                                                       7.0 cm/cm    7-8 cm/cm                                          thermal expansion                                                                           °C. × 10.sup.-5                                                               °C. × 10.sup.-5                       Total light   87%          92%                                                transmittance                                                                 ______________________________________                                    

The adhesive used was a clear liquid polyurethane adhesive as commonlyavailable for bonding polycarbonate to itself, glass or metal; it had anelongation of about 300%, and was applied at a thickness of 2 mm.

As can be seen from the above, best results were obtained when the outeracrylic sheet is about 8 mm, the inner polycarbonate resin sheet 3 isabout 10 mm, and the transparent adhesive layer 4 in between istransparent polyurethane adhesive having a thickness of about 2 mm.Preferably, each of the two sheets 2, 3 includes a scratch-resistantcoating (many of which are known) on the face thereof not bonded to theother sheet.

FIG. 1 illustrates the transparent panel of a flat configuration, suchas may be used for side windows on a vehicle, building windows, windowsfor protective cages, and the like. FIG. 2 illustrates the panel of thesame construction as that illustrated in FIG. 1, but of a curvedconfiguration, such as may be used for the front and/or back windshieldsof a vehicle.

FIGS. 3 and 4 illustrate a method, and FIG. 5 illustrates a press usefulin the method, for making the curved panel of FIG. 2, but it will beappreciated that the method and press could also be used for making theflat panel of FIG. 1.

Thus each of the two resin sheets 2, 3 for making the panel is first cutaccording to the size and configuration of the panel to be produced, andis then precurved according to the curvature of the panel to beproduced. FIG. 3 illustrates how each of the two resin sheets 2, 3 isprecurved according to the curvature, e.g., of a windshield to beapplied to a vehicle.

Thus, as shown in FIG. 3, a sheet of acrylic resin 2, having dimensionsslightly larger than those of the windshield is supported on an actualglass windshield having the desired curvature (and serving as thereference model), and is heated to a temperature of about 140° C. Thistemperature is sufficiently high to soften the acrylic resin, but notthe glass windshield 10. Accordingly, the acrylic resin sheet willassume the curvature of the glass windshield 10.

A sheet 3 of polycarbonate resin, also having dimensions slightly largerthan those of the windshield 10, is supported on the windshield and isheated to a temperature of about 150° C. This temperature is sufficientto soften the polycarbonate resin sheet 3, but not the glass windshield10, so that the polycarbonate resin sheet 3 thus also assumes thecurvature of the glass windshield.

The curved acrylic resin sheet 2 is then supported with its concave facefacing upwardly. A preformed sealing strip 4 is applied around theperipheral edge of the acrylic resin sheet 2. The polycarbonate resinsheet 3 is then applied over the sealing strip 4 so as to be spaced fromthe acrylic resin sheet 2 by the thickness of the sealing strip, 2 mm inthis case. Two holes 12, 14 are drilled through the polycarbonate resinsheet 3 adjacent to two diagonal corners of the sheet (e.g., see FIG.1). Pressure is then applied (FIG. 4) to the opposite faces of the twosheets to press them against the sealing strip 4, while an adhesiveliquid 16 is injected under pressure through one hole (e.g., 12) untilit is seen exiting from the other hole (e.g., 14), thereby assuring thatthe complete space between the two sheets 2, 3 is filled with theadhesive 6. The adhesive is then permitted to harden to bond the twosheets together.

The press illustrated in FIGS. 5 and 6, and therein designated 18, isused for applying the pressure to the two sheets at the time ofinjection of the adhesive liquid 16 between the two sheets, to preventdistortion of the two sheets by the pressure of the injected liquid.Press 18 illustrated in FIG. 5 comprises a fixed frame assembly,generally designated 20, and a movable frame assembly, generallydesignated 30, movable to an open position or to a closed position withrespect to the fixed assembly 20. Both assemblies are of rectangularconfiguration of a size at least as large as, but preferably largerthan, the largest panel to be produced.

The fixed frame assembly 20 comprises four vertical bars 21, one at eachof the four corners of the frame assembly, joined together by four lowerhorizontal bars 22 braced by a diagonal bar 23, and four upper bars 24which may be similarly braced by a diagonal bar (not shown). The fixedframe assembly 20 further includes a plurality of parallel pressure bars25 extending transversely across the assembly for contacting the lowersurface of the sheets to be bonded together and occupying the completearea of such sheets. Each of the pressure bars 25 includes an outerliner 26 (FIG. 6) of rubber or other resilient cushioning material whichdirectly contacts the lower surface of the acrylic sheet to thepolycarbonate sheet.

Each of the pressure bars 25 is mounted to the fixed frame assembly 20by a cylinder-piston device 27 at each of the opposite ends of thepressure bar. The piston-cylinder devices permit each pressure bar to belocated at a precise vertical position according to the curvature of thesheets to be bonded together.

The movable frame assembly 30 includes a rectangular frame of fourhorizontal bars 31 and four vertical bars 32 at the four cornerstelescopingly receivable within the vertical bars 21 of the fixed frameassembly 20, to permit the movable frame assembly 30 to be moved to anopen position away from the fixed frame assembly, or to a closedposition towards the fixed frame assembly. The movement of the movableframe assembly 30 is effected by four cylinder-piston devices 33 at thefour corners of the press, each coupling one of the fixed vertical bars21 to one of the movable vertical bars 32.

The movable frame assembly 30 further includes a plurality of parallel,horizontal pressure bars 35 extending transversely of the assembly, onefor and aligned with one of the pressure bars 25 of the fixed frameassembly 20. Each of the pressure bars 35 is also mounted by a pair ofcylinder-piston devices 36, permitting each such bar to be moved to apreselected vertical position, according to the curvature of the panelto be produced. The cylinder-piston devices 36 are mounted to an upperframework including four further horizontal bars 37.

As indicated earlier, the two groups of pressure bars 25 and 35 are eachindividually movable by their respective cylinder-piston devices 27 and37 to appropriate vertical positions in accordance with the curvature ofthe panel to be produced. The pressure bars 25, 35 are moved to theirrespective vertical positions by a plurality of handles 40, onecontrolling all the cylinder-piston devices of one pressure bar 25 inthe fixed frame assembly 20, and the aligned pressure bar 35 in themovable frame assembly 30. When the movable frame assembly 30 is movedto its closed position with respect to the fixed frame assembly 20,handles 40 are manually actuated to permit the pressure bars to befreely moved by their respective cylinder-piston devices 27, 37 untilthey contact the surface of the panel. The pressure bars are thus movedto their respective vertical positions according to the curvature of thepanel. They are then fixed in those positions by further handles 42, onefor each pair of aligned pressure bars 25, 35. When handles 42 are movedto their closed positions, they block the flow of the fluid to therespective cylinder-piston devices 27, 37, to thereby fix the pressurebars in position.

It will thus be seen that after the precurved polycarbonate resin sheethas been placed over the sealing strip 4 applied around the outerperiphery of the acrylic resin sheet, the two sheets are then appliedbetween the pressure bars 25 of the fixed frame assembly 20 and thepressure bars 35 in the movable frame assembly 30. The movable frameassembly 30 is then moved to its closed position, and handles 40 areactuated to move the two groups of pressure bars 25, 35 into contactwith the two sheets of the panel such that the bars assume theirrespective vertical positions according to the curvature of the twosheets. The handles 42 are then actuated to block the flow of fluid fromthe cylinder-piston devices 27, 37, thereby fixing the pressure bars intheir respective vertical positions according to the curvature of thetwo sheets.

The transparent liquid adhesive is then injected via one hole (e.g., 12)in the polycarbonate resin sheet 3 under high pressure to fill the spacebetween the two sheets with the transparent adhesive, as shown at 16 inFIG. 4. The pressure injection of liquid adhesive continues until theadhesive begins to exit from the other hole 14 at a diagonally-opposedcorner from opening 12, indicating that the complete space between thetwo sheets has been filled with the transparent adhesive. The two holes12, 14 are located so as to be outside of the area covered by thepressure bars 25, 35, and thereby easily accessible for injecting theliquid adhesive. During this injection of the transparent adhesive, thetwo groups of pressure bars 25, 26 of the press illustrated in FIG. 5are fixed in their respective vertical positions and prevent anydistortion or displacement of the two sheets despite the high pressureof injection of the liquid adhesive.

After the complete space between the two sheets 2, 3 has been filledwith the transparent adhesive, the two holes 12, 14 may be plugged, andthe adhesive is permitted to harden to thereby firmly bond the twosheets together to produce the laminated assembly.

The liquid adhesive 16 is preferably one of the commercially-availablecold-applied, transparent, polyurethane adhesives. The sealing strip 4is preferably a transparent silicon tape of 2 mm thickness having atransparent polyurethane adhesive layer applied to its opposite faces.As one example, the adhesive may be formulation 1908 E.P supplied byEngineering Chemicals B.V., Steenbergen, Netherlands, and may beinjected at a pressure of about 1.5 to 2 atmospheres, although thispressure may be increased up to about 7 atmospheres in order to decreasethe injection time.

Since the laminated panel is made of plastic sheets, the margins of thesheets may be trimmed or planed to fit the frame (e.g., windshieldframe) in which they are to be applied.

FIG. 7 illustrates another form of press which may be used when applyingthe cold liquid adhesive to the two sheets. The press illustrated inFIG. 7, generally designated 50, also includes a lower fixed frameassembly 60, and an upper movable assembly 70 which is movable to eitheran open or a closed position with respect to the fixed frame assembly.The opening and Closing of the movable frame assembly 70 may also beeffected by telescoping vertical bars 61, 71 at each of the four cornersof the two assemblies and actuated by a cylinder-piston device (notshown) at each of these corners.

The fixed frame assembly 60 also includes a plurality of pressure bars65 extending transversely of the assembly and each adjustable to aselected vertical position according to the curvature of the panel to beproduced.

In the press Illustrated in FIG. 7, however, each of the pressure bars65 is lined with an inflatable flat boot 66, e.g., of rubber or thelike. The boots 66 directly contact the lower surface of the acrylicsheet used in producing the laminated panel, and apply the pressureduring the application of the liquid adhesive between the two sheets.

Press 50 illustrated in FIG. 7 also provides another arrangement foradjusting the vertical positions of the pressure bars 65 to conform tothe curvature (or flatness) of the laminated panel to be produced. Inthis case, each of the pressure bars 65 is vertically adjustable by apair of screw-and-nut devices 67 securing the opposite ends of eachpressure bar 65 to the lower frame assembly 60.

The pressure bars in the movable assembly 70, and therein designated 75,are similarly constructed and mounted as the pressure bars 66 in thefixed frame assembly 60. Thus, each pressure bar 75 in the movable frameassembly includes an inflatable flat boot 76 which directly contacts theouter surface of the polycarbonate sheet used in producing the laminatedpanel and applies pressure to that surface during the time of theinjection of the transparent adhesive. Each of the pressure bars 75 inthe movable frame assembly 70 is also mounted for vertical movement by apair of screw-and-nut devices, shown at 77, secured to the opposite endsof each pressure bar.

The press illustrated in FIG. 7 is particularly useful for producing arun of laminated panels all of the same configuration. Thus, when eachof the pressure bars 65, 75 is preset in its proper vertical position,according to the curvature (or flatness) of the laminated panel to beproduced, the same setup may be used for producing the run of laminatedpanels. The method of producing the laminated panels is the same asdescribed above with respect to the press of FIGS. 5 and 6, except thatafter the upper frame assembly 70 has been moved to its closed position,the boots 66 and 76 carried by the pressure bars 65 and 75 are inflatedto firmly contact the opposite faces of the sheets being laminated andto prevent their distortion by the high pressure of injection of thetransparent adhesive.

While the invention has been described with respect to two preferredembodiments, it will be appreciated that many other variations,modifications and applications of the invention may be made.

What is claimed is:
 1. The method of making a transparent panel, whicheffectively blocks the penetration of a bullet when fired from the outerside of a panel, but not when fired from the inner side of the panel,comprising:forming a sheet of an acrylic resin and a sheet of apolycarbonate resin of the same size and configuration; applying asealing strip completely around the peripheral edge of one of thesheets; applying the other sheet over the one sheet with the two sheetsspaced from each other by said sealing strip; drilling two holes throughone of the sheets adjacent its diagonally opposite edges; applyingpressure to the opposite faces of the two sheets to press them againstthe sealing strip; injecting under pressure an adhesive liquid throughone hole of the one sheet until it exits from the other hole thereofsuch that said liquid completely fills the volume enclosed by saidsealing strip and the two sheets; and permitting the adhesive to hardento bond the two sheets together.
 2. The method according to claim 1,wherein said sealing strip is applied completely around the peripheraledge of the acrylic resin sheet.
 3. The method according to claim 1,wherein said holes are drilled through said polycarbonate resin sheet.4. The method according to claim 1, wherein the acrylic resin sheet andthe polycarbonate resin sheet are each individually precurved to thedesired curvature by supporting the respective resin sheet on a glasspanel having the desired curvature and heating the resin sheet and glasspanel to a temperature sufficiently high to soften the respective resinsheet, but not to soften the glass panel, and thereby to cause therespective resin sheet to assume the curvature of the glass panel. 5.The method according to claim 1, wherein said pressure is applied duringinjection of the adhesive to the opposite faces of the two sheets by apress having a fixed frame assembly, and a movable frame assemblymovable with respect to said fixed frame assembly; each of said frameassemblies including a plurality of parallel pressure bars extendingtransversely across the respective frame; said press further including aplurality of adjustable devices for precisely positioning the pressurebars against opposite surfaces of the panel.
 6. The method according toclaim 5, wherein said plurality of adjustable devices include a pistonand cylinder coupled to each of the pressure bars in each of the frameassemblies.
 7. The method according to claim 5, wherein said pluralityof adjustable devices includes a manually-adjustable screw and nut foreach of the pressure bars in each of the frame assemblies.
 8. The methodaccording to claim 5, wherein each of said pressure bars includes aresilient cushioning layer for directly contacting the respectivesurface of the panel.
 9. The method of claim 5, wherein each of saidpressure bars includes an inflatable boot for directly contacting therespective surface of the panel.
 10. The method of making a transparentpanel, which effectively blocks the penetration of a bullet when firedfrom the outer side of a panel, but not when fired from the inner sideof the panel, comprising:forming a sheet of an acrylic resin and a sheetof a polycarbonate resin of the same size and configuration; applying asealing strip completely around the peripheral edge of one of thesheets; applying the other sheet over the one sheet with the two sheetsspaced from each other by said sealing strip; drilling two holes throughone of the sheets adjacent its diagonally opposite edges; applyingpressure to the opposite faces of the two sheets to press them againstthe sealing strip by a press having a fixed frame assembly, and amovable frame assembly movable with respect to the fixed frame assembly,with each of said frame assemblies including a plurality of parallelpressure bars extending transversely across the respective frame, withsaid press further including a plurality of adjustable devices forprecisely positioning the pressure bars against opposite surfaces of thepanel; injecting while under said pressure an adhesive liquid throughone hole of the one sheet until it exits from the other hole thereofsuch that said liquid completely fills the volume enclosed by saidsealing strip and the two sheets; and permitting the adhesive to hardento bond the two sheets together.
 11. The method according to claim 10,wherein said plurality of adjustable devices include a piston andcylinder coupled to each of the pressure bars in each of the frameassemblies.
 12. The method according to claim 10, wherein said pluralityof adjustable devices includes a manually-adjustable screw and nut foreach of the pressure bars in each of the frame assemblies.
 13. Themethod according to claim 10, wherein each of said pressure barsincludes a resilient cushioning layer for directly contacting therespective surface of the panel.
 14. The method of claim 10 wherein eachof said pressure bars includes an inflatable boot for directlycontacting the respective surface of the panel.